In producing documents for security applications, e.g., documents of high value or documents required for secure access or the like, it is desirable to add information into the document that prevents or at least hinders alterations and counterfeiting. In many cases, it is desirable to have this information included in a machine-readable form that cannot be encoded or decoded by an uninitiated third-party.
FIG. 1 is a greatly enlarged portion of a document D′ including a printed (background) region PR′ that is encoded according to a known glyph method so as to include information that can be used for security purposes (the printed region PR′ of FIG. 1 is an example of a known system referred to as DataGlyphs by Xerox Corporation). In the system of FIG. 1, angular modulation of a slash character (forward slash “/” or backslash “\”) is used to encode the “1” and “0” bits of a binary data stream. More particularly, a character such as a 7 bit ASCII character string is encoded by a bitstring ST′, wherein some of the bits in the bitstring represent data bits and other bits represent error-check bits such as a parity bit or hamming code bits, etc. In the DataGlyph system of FIG. 1, however, each bit of the bitstring ST′ must be individually addressed to define or decode the overall printed region PR′. With respect to decoding, this bit-by-bit processing prevents use of standard optical character recognition (OCR) software. On the other hand, an advantage of the glyph method of FIG. 1 is that the encoding is accomplished not by density (which is easily perceived by the human visual system), but instead by angular modulation of a base symbol such as a slash symbol that has first and second orientations. The slash is one preferred base symbol because neither the first nor the second orientations approach horizontal or vertical, which makes angular modulation thereof less perceptible to the human visual system, i.e., \ \ / / \ / / \ is less noticeable to humans that than the equivalent || − − | − − | when used as a background in a printed region PR'. As used herein, the term glyph is intended to mean a pattern defined by angular modulation of a single base character or symbol to encode data, with the slash character (forward slash and backslash) being one example.
It is also generally known to define a font, such as a Postscript Type 3 font or other for security applications, by creating a bitmap representation of each font character and storing same for use in a variable printing environment, e.g., Variable Data Intelligent Postscript Printware VIPP or Personalized Print Markup Language (PPML) or the like. A user can work with these fonts in conventional ways using word processing, graphic design, and other computer programs to define a digital document to be printed, and the font is then printed according to its definition (typically the font is displayed on a visual monitor in a manner that indicates its type to a user, but that does not actually show its true definition in order to make the font human readable and human useable on a computer monitor). Examples of such “security bitmap fonts” include:                a gloss mark font in which each character is defined against a same-color background grey level, wherein the background and character are defined using respective anisotropic halftone dot structures that allows for human perception of the character at certain viewing angles without being susceptible to useful reproduction by digital or analog copying;        a microtext font in which each character is defined at a size of less than 1 point, i.e., a height of less than about 0.3527 mm so as to be readable only with a loupe or magnifying glass;        a correlation mark font in which the printed characters are visible only when a transparency key (often a 50% checkerboard grid pattern) is overlaid on the page.The above mentioned examples of bitmapped effect fonts—referred to generally herein as “SI fonts”—are combined as Specialty Imaging feature in the Xerox Free Flow Variable Imaging Suite. In such case, each character of the font is precisely defined by a bitmap image to ensure proper placement of the ink/toner dots so that the desired effect is assured. In one known arrangement, a bitmap font for use in a gloss mark, microtext or correlation mark application is embedded or encapsulated in a PostScript Type 3 font format and saved at the printer, i.e., in the digital front-end (DFE) for use in such printing applications. These known SI fonts are human readable, either with the naked eye or using a tool such as a magnifier, an overlay, ultra-violet light, infra-red light, or other means.        
U.S. patent application Ser. No. 12/359,502 filed Jan. 26, 2009 entitled Font-Input Based Recognition Engine for Pattern Fonts, the entirety of which is hereby expressly incorporated by reference into the present specification, discloses defining a font using glyph-like structures corresponding respectively to various characters of the font definition, and using the font to define the background of a digital image representing a document to be printed. When printed, the glyph-like structures encode information in the document background that can be decoded using OCR methods, by making the font definition (and any encryption keys) available to the scanner or other decoding system. As shown in FIG. 2A of the present application Ser. No. 12/359,502 generally discloses a step PA1 of creating an input string IS, a step PA2 of encrypting the input string IS to derive a coded string CS, and a step PA3 of converting the coded string CS to a font string FS using the predefined glyph font definition (the font string FS is shown as simple shaded boxes for ease of representation—see the enlarged detail for example of glyph font character/structure GF). The glyph font is used in a step PA4 to print a document D on paper or other recording medium, wherein the glyph font characters define a background or other printed region of the document D.
As shown in FIG. 2B of the present application Ser. No. 12/359,502 also generally discloses a step PA6 of scanning the printed document D to extract a font string FS′ (the font string FS′ is shown as shaded boxes for ease of representation; see enlarged detail for example of glyph font character/structure GF). In a step PA7, the extracted font string FS′ is subjected to an OCR process that uses the glyph font definition to derive a coded string CS′. In a step PA8, the coded string CS′ is decoded using a known key to derive an input string IS′. In a step PA9, the input string IS′ is compared with the expected/required input string IS. If the input string IS′ does not match the expected input string IS, the document is known to be counterfeit or otherwise defective.
This prior application Ser. No. 12/359,502 does not disclose a preferred design for the glyph font characters/structures GF. In particular, without a proper design, the need for redundancy results in groups of slashes that trigger the above-noted characteristics of the human visual system to become active in an effort to group and decode the slashes, which causes the font characters to become distracting and noticeable when used as a document background, and can also decrease security due to the presence of obvious repeating patterns. As such, it has been deemed desirable to provide a system and method for designing and using glyph font structures for enhanced security, aesthetics, customer exclusivity, and other real-world issues.